The present invention relates to the field of ultrasonics. More specifically, this invention relates to an apparatus for simultaneously cutting, sealing and stitching thermoplastic material using an ultrasonic horn assembly.
Ultrasonic energy has long been employed to both melt and cut metallic or non-metallic thermoplastic materials. In a typical application, high frequency currents are applied to a transducer which converts electrical energy into mechanical energy in the form of vibrations in the ultrasonic horn. The exact orientation of these vibrations will depend on the particular shape and structural characterisitics of the horn. The most prevalent horn used for cutting takes the shape of a tapered cone. Such a horn will insure a concentration of longitudinal vibrations at the horn tip.
When the tip of the horn is biased against a rigid material such as metal, the longitudinal vibrations at the horn tip will transfer vibrational energy to the metal at the point of contact. Frictional forces induced within the metal work pieces will then heat the metal and thereby produce the desired cut.
This procedure will not be successful when the material to be cut is a flexible thermoplastic. In such a case the vibrations transferred from the tip of the horn to the thermoplastic material will be widely distributed throughout the material. As such, the friction induced in any one section of the material will not be sufficient to produce adequate heating. In order to overcome this problem, a rigid anvil may be utilized to concentrate the transferred mechanical energy in a small swatch of the thermoplastic material. In a typical application, a flat faced anvil having a surface area smaller than that of the horn tip will be used to firmly press the flexible thermoplastic material against the face of the horn tip. In this way, substantially all of the vibrational energy transferred to the material will be concentrated in the area defined by the face of the anvil. The internal frictional forces between the fibers of the thermoplastic material will thereby melt the material along the surface defined by the face of the anvil. If the area of concentration is sufficiently small, the heat will be sufficiently intense to actually cut the material being worked on.
The above characteristics of ultrasonic horns are well-known in the art and have been employed to provide stitch seams in thermoplastic sheet-like elements. One such application can be found in U.S. Pat. No. 3,666,599 issued to Edward G. Obeda. The present invention exceeds the level of the prior art by providing a fully automatic apparatus which can simultaneously cut, seal and stitch thermoplastic material.